[Juan R.]

In perturbative string theory, spacetime is a manifold M mathematically defined like

M = N x R^4

where N is a Calabi-Yau manifold.

In M-theory (non perturbative regime), spacetime is a manifold M mathematically defined like

M = N´ x R^4

where N´ is a G2 manifold. There is really few known about these manifolds even in mathematics (compared with famous CY). You can see that there is much more information about CY.

For some elementary information can see

http://www.explore-math.com/mathemat..._manifold.html

http://encycl.opentopia.com/term/G2_manifold

I don't know much about these but I still can sure you that they will do not work (M-theorists think that topology of universe may be explained by a G2)

I don't know the details of G2 manifolds but i know that are again an archaic choosing for explaining universe because also are usual differentiable manifolds like famous CY and therefore cannot explain spacetime foam.

Again string M-theory is a disaster like an irrelevant attempt to theory of everything.

[Guille]

Juan R,

Thanks for the information.

[Dave_M]

You people.. i forget who it was now was saying that "shouldnt time dissapear".. no.. time isnt a thing its a measure or the daily cycle..
nothing to hard.. if im wrong tell me

[pramodmaths]

The G2 manifolds are the manifolds with holonomy as the one of the exceptional lie groups that is G2 group.
u can get a tasi lecture pdg on the internet via arxiv or google search itself